Wireless control systems are used in many different applications to provide a method of remote control of devices or systems. Wireless control systems, such as garage door opener systems, home security systems, gate controllers, etc., typically employ a portable, hand-held transmitter (i.e., an original transmitter) to transmit a control signal to a receiver located at a remote system or device. For example, a garage door opener system typically includes a receiver located within a home owner's garage and coupled to the garage door opener. A user presses a button on the original transmitter to transmit a radio frequency signal to the receiver to activate the garage door opener to open and close a garage door. Accordingly, the receiver is tuned to the frequency of its associated original transmitter and demodulates a predetermined code programmed into the original transmitter and the receiver for operating the garage door.
To enhance security of wireless control systems, such as a garage door opener system, manufacturers commonly use encryption technology to encrypt the radio frequency signal sent from a transmitter to a receiver. One such encryption method is a rolling code system, where each digital message sent from the transmitter to the receiver has a different code from the previous digital message. In one such system, a transmitter identifier (sometimes called a serial number) and an encrypted counter value (sometimes called a hop code) are sent with each transmission. A counter value in the transmitter increments each time the transmitter button is pressed. An encryption algorithm encrypts the counter value to create a new encrypted code or value. When the encrypted counter value is transmitted, it appears to bear no predictable relationship to the previously sent encrypted counter value, and thereby appears to “hop” from one value to another. The receiver also stores the counter value in unencrypted form. Upon receipt of an encrypted counter value for a particular transmitter identifier, the counter value is unencrypted and compared to the previously stored counter value to determine whether the garage door opener should be activated. If the new value is less than or the same as the previously stored counter value, it may have come from a code grabber, and, therefore, the receiver does not activate the garage door opener. If the new value is greater than the previously stored counter value but less than a predefined number, the garage door is activated. If the new value is greater than the predefined number ahead of the previously stored counter value, the receiver stores the value, but does not activate the garage door opener. Upon receipt of the next counter value from the transmitter, if the receiver determines that the two values are in sequence, the garage door is activated and the most recently received counter value is stored in memory. The system described above is just one example of many types of rolling code based systems.
As an alternative to a portable, hand-held original transmitter, a trainable (or universal) transmitter or transceiver may be provided in, for example, a vehicle, for use with remote control devices or systems. An example of a trainable or universal transmitter is the HomeLink® trainable transmitter manufactured by Johnson Controls Interiors, LLC, Holland, Mich. A trainable transmitter may be configurable by a user to activate one or more of a plurality of different receivers using different radio frequency messages. In one example, a trainable transmitter may be trained to an existing original transmitter for a wireless control system by holding the two transmitters in close range and pressing buttons on the original transmitter and trainable transmitter simultaneously. The trainable transmitter identifies the type of wireless control system associated with the original transmitter based on the radio frequency signal received from the original transmitter. The trainable transmitter may then identify and store the control data and RF carrier frequency of the original transmitter radio frequency control signal. For systems employing a rolling code (or other encryption method), the trainable transmitter and wireless control system receiver are then synchronized so that, for example, the counters of the trainable transmitter and the receiver begin at the same value. Once trained, the trainable transmitter may be used to transmit RF signals to the receiver to control the wireless control system.
An original transmitter or trainable transmitter is configured to send a control signal at the frequency to which the receiver of a wireless control system is tuned. If, however, a wireless control system is dual- or multiple-frequency (i.e., capable of operating at one of multiple frequencies), it is possible that certain existing trainable transmitters or receivers may not be compatible with one or more of the operating frequencies of the wireless control system. Such a problem may also occur when a manufacturer of a wireless control system changes the frequency of operation for new versions of the wireless control system. Accordingly, there is a need for a transmitter that is capable of transmitting an RF control signal at two frequencies in response to a single user input. Further, there is a need for a transmitter that is configured to, in response to a single user input, transmit a rolling code message at a first frequency and to transmit the same rolling code message at a second frequency.